Power supply system and short circuit and/or bad connection detection method thereof, and power converter thereof

ABSTRACT

The present invention discloses a short circuit and/or bad connection detection method for use in a power supply system. The power supply system includes a power converter which converts an input voltage to an output voltage and supplies an output current to an electronic device. In the short circuit detection method, the conversion from the input voltage to the output voltage is disabled in a disable time period, and whether a short circuit occurs is determined according to the decreasing speed of the output voltage. In the bad connection detection method, an actual voltage and an actual current received by the electronic device are compared with the output voltage and the output current, to determine whether a bad connection occurs.

CROSS REFERENCE

The present invention claims priority to U.S. 62/014,305, filed on Jun.19, 2014.

BACKGROUND OF THE INVENTION

Field of Invention

The present invention relates to a power supply system capable ofperforming a short circuit detection and a bad connection detection;particularly, it relates to such a power supply system capable ofdetecting abnormal but not severe conditions which lead to undesirablepower loss, such as weakly short circuit and weakly bad connectionconditions, and a detection method and a power converter thereof.

Description of Related Art

Please refer to FIGS. 1A and 1B. FIG. 1A shows a block diagram of aconventional power supply system. FIG. 1B explains how an abnormal butnot severe condition occurs in the prior art of FIG. 1A which leads topower loss. The conventional power supply system 10 comprises a powerconverter 11, a cable 12 and an electronic device 13. A port 112 of thepower converter 11 is connected to a port 121 of the cable 12. A port132 of the electronic device 13 is connected to another port 122 of thecable 12. When the power converter 11, the cable 12 and the electronicdevice 13 are connected in serial, power lines 17 and 18 form a loop todeliver the power. The cable 12 further includes a signal line 14, fordata transmission between the power converter 11 and the electronicdevice 13. The signal line 14 can be, for example but not limited to, adifferential signal line.

As shown in FIG. 1B, when an unwanted material such as dust, dirt,thread, etc. falls on or in the ports 112, 121, 122 and/or 132, thepower lines 17 and 18 may be “weakly short-circuited”—i.e., a short-cutcurrent path is formed between the power lines 17 and 18, but theelectrical connection is weak, so there is not a huge amount of currentflowing through this short-cut current path. Such “weakly short circuit”is illustrated by the resistors R11, R121, R122 and R13 in the figure.Although there is not a huge amount of current flowing through theshort-cut current path, this abnormal condition still leads to powerloss, and if this abnormal condition is not well controlled, it can bevery dangerous.

Besides, if the power lines 17 and 18 does not have a good quality, or abad connection occurs between the ports, even though the bad connectionis not so severe to cause an open-circuit, this abnormal condition willalso lead to power loss. The bad connection is illustrated by theresistors R1′, R2′, R3′ and R4′ in the figure.

Because the “weakly short circuit” and “bad connection” usually do notlead to fully short-circuit or complete open-circuit, the prior art didnot propose an effective solution to address this issue.

The prior art U.S. Pat. No. 8,498,087 and U.S. Pat. No. 8,339,760provide an approach to solve the above-mentioned problem by detectingwhether there is abnormal temperature increase in the cable. However, todo so, an additional heat detection signal line is required, which isnot compatible to the current standard cable, and also leads to a highermanufacturing cost. Moreover, before an abnormal temperature increasebecomes detectable, unwanted power loss and other problems have alreadyhappened for a long time. Therefore, the above-mentioned prior artpatents do not practically solve the problem.

In view of the above, to overcome the drawbacks in the prior art, thepresent invention proposes a power supply system capable of detecting anabnormal condition such as a weakly short circuit and a bad connection,which leads to undesirable power loss.

SUMMARY OF THE INVENTION

From one perspective, the present invention provides a power converterfor converting an input voltage to an output voltage, wherein the outputvoltage is to be supplied to an electronic device through a cable; thepower converter comprising: a switch; a switch control unit forcontrolling the switch, to perform the conversion from the input voltageto the output voltage; and a short circuit detection unit, including: atimer circuit for generating a temporary stop signal, to temporarilydisable the switch control unit for a disable time period; and anabnormal voltage drop detection circuit for determining whether or not ashort circuit occurs during the disable time period according to adecreasing speed of the output voltage.

In one embodiment, the abnormal voltage drop detection circuit includes:a voltage comparison circuit for determining whether or not the shortcircuit occurs according to a comparison result between the outputvoltage and a reference voltage.

In one embodiment, the reference voltage is adjustable.

In one embodiment, when the power converter is coupled to the electronicdevice through the cable, the reference voltage is set to a relativelylower level; and when the power converter is not coupled to theelectronic device through the cable, the reference voltage is set to arelatively higher level.

In one embodiment, the power converter includes an isolated type AC-DCconverter, and the isolated type AC-DC converter transmits a feedbacksignal related to the output voltage to the switch control unit via afeedback circuit, wherein the temporary stop signal disables the switchcontrol unit by turning off the feedback circuit.

In one embodiment, the timer circuit generates the temporary stop signalby one or a combination of two or more of the following approaches:generating the temporary stop signal STOP during or immediately after astart-up operation; generating the temporary stop signal STOP during orimmediately after a power-on-reset operation; generating the temporarystop signal STOP periodically; or generating the temporary stop signalSTOP irregularly.

From another perspective, the present invention provides a short circuitdetection method of a power supply system, wherein the power supplysystem includes a power converter for converting an input voltage to anoutput voltage to be supplied to an electronic device through a cable;the short circuit detection method of the power supply system comprisingthe steps of: stopping converting the input voltage to the outputvoltage for a disable time period; and determining whether or not ashort circuit occurs according to a decreasing speed of the outputvoltage.

From another perspective, the present invention provides a power supplysystem, comprising: a power converter for converting an input voltage toan output voltage and supplying an output current, wherein the outputvoltage and the output current are supplied to an electronic devicethrough a cable; and a bad connection detection unit, including: avoltage sensing circuit for sensing an actual voltage received by theelectronic device; a current sensing circuit for sensing an actualcurrent received by the electronic device; a first analog-to-digitalconverter for converting the actual voltage to a first digital signal; asecond analog-to-digital converter for converting the actual current toa second digital signal; and a calculation circuit for determiningwhether or not a bad connection occurs according to the first digitalsignal, the second digital signal, the output voltage and the outputcurrent.

In one embodiment, the calculation circuit compares the first digitalsignal with a desired level of the output voltage and compares thesecond digital signal with a desired level of the output current, todetermine whether or not the bad connection occurs.

In one embodiment, the calculation circuit compares the first digitalsignal with a digital signal of the output voltage converted from asensed value of the output voltage and compares the second digitalsignal with a digital signal of the output current converted from asensed value of the output current, to determine whether or not the badconnection occurs.

In one embodiment, the bad connection detection unit is located insidethe electronic device.

In one embodiment, the bad connection detection unit has a first partinside the electronic device and a second part inside the powerconverter, and the first and second parts of the bad connectiondetection unit communicate through a signal line of the cable.

From another perspective, the present invention provides a badconnection detection method of a power supply system, wherein the powersupply system includes a power converter for converting an input voltageto an output voltage and supplying an output current, the output voltageand the output current being supplied to an electronic device through acable, the bad connection detection method of the power supply systemcomprising the steps of: sensing a actual voltage and an actual currentreceived by the electronic device and converting the actual voltage andthe actual current to an actual voltage digital signal and an actualcurrent digital signal, respectively; comparing the actual voltagedigital signal and the actual current digital signal with a desiredlevel of the output voltage and a desired level of the output current,respectively; and when a difference between the actual voltage digitalsignal and the desired level of the output voltage exceeds a firstpredetermined threshold difference, and/or when a difference between theactual current digital signal and the desired level of the outputcurrent exceeds a second predetermined threshold difference, determiningthat a bad connection occurs.

From another perspective, the present invention provides a badconnection detection method of a power supply system, wherein the powersupply system includes a power converter for converting an input voltageto an output voltage and supplying an output current, the output voltageand the output current being supplied to an electronic device through acable, the bad connection detection method of the power supply systemcomprising the steps of: sensing a actual voltage and an actual currentreceived by the electronic device and converting the actual voltage andthe actual current to an actual voltage digital signal and an actualcurrent digital signal, respectively; sensing the output voltage and theoutput current and converting the output voltage and the output currentto an output voltage digital signal and an output current digitalsignal, respectively; comparing the actual voltage digital signal andthe actual current digital signal with the output voltage digital signaland the output current digital signal, respectively; and when adifference between the actual voltage digital signal and the outputvoltage digital signal exceeds a first predetermined thresholddifference, and/or when a difference between the actual current digitalsignal and the output current digital signal exceeds a secondpredetermined threshold difference, determining that a bad connectionoccurs.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below, with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a block diagram of a conventional power supply system.

FIG. 1B explains how an abnormal condition occurs in the prior art ofFIG. 1A which leads to power loss.

FIGS. 2A-2B show a block diagram of a power supply system according to afirst embodiment of the present invention.

FIG. 2C shows an embodiment of a power converter.

FIGS. 3A-3B show a block diagram of a power supply system according to asecond embodiment of the present invention.

FIGS. 4A-4B show a block diagram of a power supply system according to athird embodiment of the present invention.

FIG. 5A shows an embodiment of a short circuit detection unit.

FIG. 5B explains how the present invention performs the short circuitdetection.

FIG. 6A shows another embodiment of a short circuit detection unit.

FIGS. 6B-6C show two embodiments as to how the present inventiongenerates a temporary stop signal.

FIGS. 7A-7C explain an embodiment as to how the present inventionperforms the bad connection detection.

FIGS. 7D-7E show two embodiments as to how the present inventionperforms the bad connection detection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above and other technical details, features and effects of thepresent invention will be will be better understood with regard to thedetailed description of the embodiments below, with reference to thedrawings. The drawings as referred to throughout the description of thepresent invention are for illustration only, to show the interrelationsbetween the components and devices, but not drawn according to actualscale.

Please refer to FIGS. 2A-2C, FIGS. 3A-3B and FIGS. 4A-4B. FIG. 2A showsa block diagram of a power supply system according to a first embodimentof the present invention. FIG. 2B shows a circuit diagram of FIG. 2A.FIG. 2C shows an embodiment of a power converter. In FIGS. 2A-2C, thepower converter is not coupled to a cable. FIG. 3A shows a block diagramof a power supply system according to a second embodiment of the presentinvention. FIG. 3B shows a circuit diagram of FIG. 3A. In FIGS. 3A-3B,the power converter is coupled to a cable. FIG. 4A shows a block diagramof a power supply system according to a third embodiment of the presentinvention. FIG. 4B shows a circuit diagram of FIG. 4A. In FIGS. 4A-4B,the power converter and the electronic device are coupled to each otherthrough a cable.

In one embodiment, the power converter 21 has not yet been connected toany other device or component (as shown by the power supply system 20 inFIG. 2B). As shown in FIG. 2B, the power converter 21 has one port 212.In another embodiment, the power converter 21 has already been connectedto a cable 22 but has not yet been connected to an electronic device (asshown by the power supply system 30 in FIG. 3B). As shown in FIG. 3B, aport 212 of the power converter 21 is connected to a port 221 of thecable 22. In still another embodiment, the power converter 21, the cable22 and the electronic device 23 have already been connected in serial(as shown by the power supply system 40 in FIG. 4B). A port 212 of thepower converter 21 is connected to a port 221 of the cable 22, and aport 232 of the electronic device 23 is connected to a port 222 of thecable 22.

Please refer to FIG. 2C. The power converter 21 can be, for example butnot limited to, an isolated type AC-DC converter. Note that the powerconverter 21 shown in FIG. 2C is for illustrative purpose only, but notfor limiting the scope of the present invention. The power converter 21can be any other type of power converter. In the isolated type AC-DCconverter shown in FIG. 2C, the power converter 21 includes atransformer 213 having a primary side 213 a and a secondary side 213 b.The primary side 213 a is coupled to a switch SW which is controlled bya switch control unit 214. The secondary side 213 b is coupled to anoutput unit 210, which generates a feedback signal FB according to anoutput voltage Vout, and provides the feedback signal FB through afeedback circuit 215 (e.g., an opto-coupler circuit) to the switchcontrol unit 214. In normal operation, the switch control unit 214controls the switch SW according to the feedback signal FB, to convertan input voltage Vin to the output voltage Vout at the secondary side213 b. The output unit 210 includes a short circuit detection unit 211,to detect whether a short circuit or even a weakly short circuit occurs.The details for the short circuit detection unit 211 will be describedlater. The basics of an isolated type AC-DC converter are well known tothose skilled in the art, so for the sake of simplicity, only thecircuits relevant to the present invention are illustrated whereas othercircuits irrelevant to the present invention are omitted.

Note that the power converter 21 is not limited to an isolated typeAC-DC converter, yet it can also be another type of switching powerconverter such as a synchronous or asynchronous boost, buck, buck-boostor inverting power converter. Among these switching power converters(including the isolated type AC-DC converter), they all have a switchcontrol unit, which controls at least one switch according to thefeedback signal, to convert the input voltage to the output voltage. Thepresent invention is applicable to anyone of these switching powerconverters. The short circuit detection unit can be located at anyappropriate location within the switching power converter, which, whendetecting that a short circuit or a weakly short circuit occurs, issuesan error signal Error 1 to the switch control unit.

Please refer to FIGS. 3A-3B and FIGS. 4A-4B. Unlike the embodiment shownin FIGS. 2A-2C, the power converter 21 shown in FIGS. 3A-3B has alreadybeen connected to a cable 22. And, in embodiment shown in FIGS. 4A-4B,the power converter 21 is connected to the cable 22 and the cable 22 isconnected to the electronic device 23. In the embodiment shown in FIGS.4A-4B, in normal operation, the power lines 27 and 28 form a loop, sothat power can be delivered to the electronic device 23. The cable 22further includes a signal line 24, for data transmission between thepower converter 21 and the electronic device 23. The signal line 24 canbe, for example but not limited to, a differential signal line.

As shown in FIGS. 2B, 3B and 4B, when there is an unwanted material suchas dust falling on or in the ports 212, 221, 222 and/or 232, a short-cutcurrent path is formed between the power lines 17 and 18, but theelectrical connection is weak, so there is not a huge amount of currentflowing through this short-cut current path. Such “weakly short circuit”is illustrated by the resistors R21, R221, R222 and R23 in the figures.This abnormal condition leads to power loss, and if this abnormalcondition is not well controlled, it can be very dangerous.

To overcome this drawback, the short circuit detection unit 211 of thisembodiment can detect whether a short circuit abnormal condition occurs,so that necessary procedures can be taken as soon as possible.

FIGS. 5A-5B shows an embodiment of the short circuit detection unit 211.Regardless whether the power converter 21 is connected to the cable 22and regardless whether the cable 22 is connected to the electronicdevice 23, this embodiment can be adopted to check whether a shortcircuit abnormal condition occurs.

Please refer to FIGS. 5A-5B. The short circuit detection unit 211 ofthis embodiment includes a timer circuit 2112 and an abnormal voltagedrop detection circuit 2114. The timer circuit 2112 counts timeaccording to a clock signal CLK, to generate a temporary stop signalSTOP which lasts for a period of time, i.e., the disable time periodTdis. (“To generate a temporary stop signal STOP” means to set the levelof the temporary stop signal STOP to a predefined level, such as a highlevel or a low level of a digital signal). In this embodiment, the timercircuit 2112 periodically generates the temporary stop signal STOP. Inother embodiments, the temporary stop signal STOP can be triggered andgenerated by other mechanisms (which will be described later). The clocksignal CLK can be obtained from a clock signal inside the powerconverter 21; or, it can be obtained from an oscillator (not shown).When the temporary stop signal STOP is generated, the switch controlunit 214 is disabled, so that the power converter 21 does not operate toconvert the input voltage Vin to the output voltage Vout. The switchcontrol unit 214 can be disabled by various ways, and the presentinvention is not limited to anyone of these ways. This embodiment showsone example: if the power converter 21 is isolated type AC-DC converter,it usually uses a feedback circuit 215 (e.g., an opto-coupler circuit)to transmit the feedback signal FB. The temporary stop signal STOP canbe used to disable the feedback circuit 215. Because the isolated typeAC-DC converter adopts a negative feedback mechanism, when the feedbackcircuit 215 does not operate, the switch control unit 214 will judgethat the output voltage Vout is sufficient, so as not to proceed theoperation to convert the input voltage Vin to the output voltage Vout,and this is equivalent to disabling the switch control unit 214. If thepower converter 21 is another type of switching power converter, theswitch control unit 214 can be disabled by any suitable way. The disabletime period Tdis in which the temporary stop signal STOP disables theswitch control unit 214 is shown in FIG. 5B.

While the temporary stop signal STOP disables the switch control unit214, the timer circuit 2112 enables the abnormal voltage drop detectioncircuit 2114 by an enable signal EN. Therefore, the temporary stopsignal STOP and the enable signal EN can be the same signal, or onebeing an inverted signal of the other. Certainly, in another embodiment,the temporary stop signal STOP and the enable signal EN can be twodifferent signals, and the enable signal EN can start slightly laterthan the temporary stop signal STOP. Being enabled, the abnormal voltagedrop detection circuit 2114 determines whether the output voltage Voutdrops abnormally according to a decreasing speed of the output voltageVout.

Please refer to FIG. 5B. During the disable time period Tdis, the powerconverter 21 does not operate to convert the input voltage Vin to theoutput voltage Vout. However, because there is a normal depletion ofcharges, the output voltage Vout will drop slowly. Hence, a thresholdline can be set, based upon a reasonable decreasing speed of the outputvoltage Vout. If the decreasing speed of the output voltage Vout isfaster and than the threshold line, it can be judged that an undesirableshort circuit occurs.

Please refer to FIG. 6A in conjugation with FIG. 5B. In one embodiment,the abnormal voltage drop detection circuit 2114 includes a voltagecomparison circuit 2114 a, which compare the output voltage Vout with areference voltage Vdis (in circuit design, an equivalent approach is tocompare a divided voltage of the output voltage Vout with a proportionalvalue of the reference voltage Vdis). In normal operation, the outputvoltage Vout will not drop below the reference voltage Vdis during thedisable time period Tdis (as shown by the line A in FIG. 5B).Nevertheless, if the output voltage Vout is below the reference voltageVdis during the disable time period Tdis (as shown by the line B in FIG.5B), it indicates that, in addition to the normal depletion of thecharges, there must be a short circuit. Under such circumstance, thevoltage comparison circuit 2114 a outputs the error signal Error 1 toreflect that a short circuit has occurred.

The abnormal voltage drop detection circuit 2114 can detect andcalculate the decreasing speed of the output voltage Vout by any otherway instead of adopting the voltage comparison circuit. For example, theabnormal voltage drop detection circuit 2114 can detect the outputvoltage Vout at two different time points, to obtain a dropping slope ofthe output voltage Vout (i.e., the slope of line A or line B); thedropping slope can be compared with the slope of the threshold line.Adopting the voltage comparison circuit to detect and calculate thedecreasing speed of the output voltage Vout is a relatively simplerapproach; however, any other approach to detect and calculate thedecreasing speed of the output voltage Vout is still within the scope ofthe present invention.

As compared to the case wherein the power converter 21 is not connectedto the electronic device 23 through the cable 22, in the case whereinthe power converter 21 is connected to the electronic device 23 throughthe cable 22, the normal depletion of charges is relatively higher.Under such circumstance, in one embodiment, the reference voltage Vdiscan be set to a relatively lower level. There are many ways to adjustthe setting of the reference voltage Vdis, and the present invention isnot limited to anyone of these ways. For example, when the powerconverter 21 is connected to the electronic device 23 through the cable22, usually, the electronic device 23 will transmit signals through thesignal line 24 to confirm the connection status, or to communicate forother purposes. Therefore, for example, the short circuit detection unit211 can set the reference voltage Vdis to a relatively lower level whenthe signal line 24 transmits a signal verifying that the power converter21 is connected to the electronic device 23 through the cable 22. On thecontrary, when the signal line 24 does not transmit a signal verifyingthat the power converter 21 is connected to the electronic device 23through the cable 22, the short circuit detection unit 211 can set thereference voltage Vdis to a relatively higher level. However, that thereference voltage Vdis is adjustable is only preferred but notnecessary. Certainly, it is also practicable and within the scope of thepresent invention that the reference voltage Vdis is a constant.

Besides adjusting the reference voltage Vdis according to whether or notthe electronic device 23 is connected to the power converter 21 throughthe cable 22, in another embodiment of the present invention, theduration of the disable time period Tdis can be adjusted. For example,in the case wherein the power converter 21 is connected to theelectronic device 23 through the cable 22, the normal depletion ofcharges is relatively higher. Under such circumstance, the duration ofthe disable time period Tdis can be shortened, for example by changingthe frequency of the clock signal CLK or the time count of the timercircuit.

In the embodiment shown in FIG. 6B, the temporary stop signal STOP isperiodically generated, which is only one example. In other embodiments,the temporary stop signal STOP can be generated during (or immediatelyafter) a start-up operation or a power-on-reset operation, or, thetemporary stop signal STOP can be generated irregularly during normaloperation. For example, please refer to FIG. 6C, typically, a Power OnReset (POR) signal is generated during a start-up operation or apower-on-reset operation, and the temporary stop signal STOP can begenerated according to this POR signal. For another example, thetemporary stop signal STOP can be generated can be set randomly. Thus,the present invention can generate the temporary stop signal STOP by oneor a combination of two or more of the following approaches: generatingthe temporary stop signal STOP during (or immediately after) a start-upoperation; generating the temporary stop signal STOP during (orimmediately after) a power-on-reset operation; generating the temporarystop signal STOP periodically; or generating the temporary stop signalSTOP irregularly (for example, the temporary stop signal STOP can begenerated not only periodically but also irregularly).

FIGS. 7A-7C show another embodiment of the present invention, which showthe bad connection detection unit and explain how the present inventionperforms a bad connection detection. The bad connection needs to bedetected only when the power converter 21 is connected to the cable 22and the cable 22 is connected to the electronic device 23, so this iswhat is shown in FIGS. 7A-7C.

Please refer to FIG. 7B. Although what the power converter 21 providesis the output voltage Vout, the voltage actually received by theelectronic device 23 is the actual voltage Vp because of the badconnection (which is expressed by resistors R1, R2, R3 and R4).Likewise, although what the power converter 21 provides is the outputcurrent Iout, the current actually received by the electronic device 23is the actual current Ip because of the bad connection. The badconnection detection unit 235 is provided to detect whether a badconnection occurs.

As shown in FIGS. 7B-7C, the bad connection detection unit 235 of thisembodiment can be, for example but not limited to, located inside theelectronic device 23. The bad connection detection unit 235 includes avoltage sensing circuit 2351, a current sensing circuit 2352, ananalog-to-digital converter (ADC) 2353, an analog-to-digital converter(ADC) 2354, and a calculation circuit 2355. The voltage sensing circuit2351 senses the actual voltage Vp, which is then converted to a digitalsignal by the ADC 2353. The current sensing circuit 2352 senses theactual current Ip, which is then converted to a digital signal by theADC 2354. The calculation circuit 2355 performs calculation according tothe outputs from the ADC 2353 and ADC 2354. In one embodiment,information of the target level of the output voltage Vout and thetarget level of the output current Iout is given by the electronicdevice 23, via the signal line 24 in the cable 22, to the powerconverter 21. Under such circumstance, because the electronic device 23has already known the target levels of the output voltage Vout and theoutput current Iout, these levels can be pre-stored in the calculationcircuit 2355. The calculation circuit 2355 can compare the outputs fromthe ADC 2353 and the ADC 2354 with the pre-stored target levels of theoutput voltage Vout and the output current Iout. When a differencebetween the target level of the output voltage Vout and the actualvoltage Vp is too large, and/or when a difference between the targetlevel of the output current Iout and the actual current Ip is too large(i.e., the difference exceeds a predetermined threshold difference), thecalculation circuit 2355 will issue an error signal Error 2 to indicatethat a “bad connection” occurs. Such error signal Error 2 can betransmitted via, for example, the signal line 24. Certainly, in otherembodiments, the error signal Error 2 can be transmitted via otherwirings (under such circumstance, the cable 22 needs to include suchwirings). Furthermore, to avoid misjudging the occurrence of a badconnection when the circuit just starts up or when the electronic device23 is in heavily loaded condition, the determination of “bad connection”can be conducted when the circuit is stable.

FIG. 7D explains another embodiment as to how the present inventionperforms a bad connection detection. In this embodiment, an ADC 2141 andan ADC 2142 are included in the power converter 21 (e.g., when the powerconverter 21 is an isolated type AC-DC converter, the ADC 2141 and theADC 2142 can be located inside the output unit 210; or, when the powerconverter 21 is another type of power converter, the ADC 2141 and theADC 2142 can be located inside the switch control unit 214). The ADC2141 and the ADC 2142 convert the output voltage Vout and the outputcurrent Iout into digital signals, respectively. The converted digitalvalues are outputted to the calculation circuit 2355 through a buffercircuit 2143. The calculation circuit 2355 compares the outputs from theADC 2353 and the ADC 2354 with the information of the output voltageVout and the output current Iout outputted from the buffer circuit 2143.When a difference between the target level of the output voltage Voutand the actual voltage Vp is too large, and/or when a difference betweenthe target level of the output current Iout and the actual current Ip istoo large (i.e., the difference exceeds a predetermined thresholddifference), the calculation circuit 2355 will issue an error signalError 2 to indicate that a “bad connection” occurs. Because the signalline 24 can transmit signals bi-directionally, the information of theoutput voltage Vout, the output current Iout and the error signal Error2 can all be transmitted via the signal line 24.

FIG. 7E explains another embodiment as to how the present inventionperforms a bad connection detection. In this embodiment, a calculationcircuit 2144 is included in the power converter 21 (e.g., when the powerconverter 21 is an isolated type AC-DC converter, the calculationcircuit 2144 can be located inside the output unit 210; or, when thepower converter 21 is another type of power converter, the calculationcircuit 2144 can be located inside the switch control unit 214). And, inthis embodiment, the bad connection detection circuit 235 furtherincludes a buffer circuit 2356 in the electronic device 23. In otherwords, the bad connection detection circuit 235 can be regarded ashaving two separate parts, located inside the power converter 21 andinside the electronic device 23, respectively. The bad connectiondetection circuit 235 outputs digital signals converted from the actualvoltage Vp and the actual current Ip, which are sent to the calculationcircuit 2144 of the switch control unit 214. The calculation circuit2144 compares the converted digital signals of the actual voltage Vp andthe actual current Ip with the converted digital values of the outputvoltage Vout and the output current Iout outputted from the ADC 2141 andthe ADC 2142, respectively. When a difference between the voltagesand/or a difference between the currents is too large (i.e., thedifference exceeds a predetermined threshold difference), thecalculation circuit 2144 will issue an error signal Error 2 to indicatethat a “bad connection” occurs.

When an abnormal condition such as a short circuit or a bad connectionis detected and the error signal Error 1 or the error signal Error 2 isgenerated, the generated error signal Error 1 or Error 2 can be used invarious ways. For example, the error signal Error 1 or Error 2 canfunction as an alarm signal to the user (e.g., the error signal Error 1or Error2 can light up an LED lamp, or trigger a buzzer to issue analert). Or, the error signal Error 1 or Error2 can maintain thetemporary stop signal STOP at the predefined level. Or, the error signalError 1 or Error2 can be used to directly disable the switch controlunit 214. Or, the error signal Error 1 or Error2 can be used to turn offthe power converter 21. Or, if the power converter 21 is an isolatedtype AC-DC converter, the error signal Error 1 or Error2 can be used toopen the path by which the secondary side of the transformer providesthe output voltage Vout. Or, the error signal Error 1 or Error2 is notused to turn off the power converter 21, but instead to limit themaximum of the output current of the power converter 21. Any or more ofthe above and other ways can be adopted, depending on practical needs.

In view of the above, the power supply system of the present inventioncan, on one hand, detect the abnormal short circuit through the shortcircuit detection unit 211 and can, on the other hand, detect theabnormal bad connection through the bad connection detection unit 235,so that power loss due to these abnormal conditions can be avoided toimprove the power utilization efficiency and better protect the circuit.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. An embodiment or a claim ofthe present invention does not need to achieve all the objectives oradvantages of the present invention. The title and abstract are providedfor assisting searches but not for limiting the scope of the presentinvention. Those skilled in this art can readily conceive variations andmodifications within the spirit of the present invention. For example,the definition of the high level and the low level of a digital signalare interchangeable, with corresponding amendments of the circuitsprocessing these signals. For another example, a device which does notsubstantially influence the primary function of a signal can be insertedbetween any two devices or circuits in the shown embodiments. For yetanother example, the cable 22 and the power converter 21 can beintegrated into a single device; or, the cable 22 and the electronicdevice can be integrated into a single device, and the spirit of thepresent invention can still be applied to such configurations. In viewof the foregoing, the spirit of the present invention should cover allsuch and other modifications and variations, which should be interpretedto fall within the scope of the following claims and their equivalents.

What is claimed is:
 1. A power converter for converting an input voltageto an output voltage, wherein the output voltage is to be supplied to anelectronic device through a cable; the power converter comprising: aswitch; a switch control unit for controlling the switch, to perform theconversion from the input voltage to the output voltage; and a shortcircuit detection unit, including: a timer circuit for generating atemporary stop signal, to temporarily disable the switch control unitfor a disable time period; and an abnormal voltage drop detectioncircuit for determining whether or not a short circuit occurs during thedisable time period in which the switch control unit has been disabledaccording to a decreasing speed of the output voltage; wherein, afterthe switch control unit has been disabled, the abnormal voltage dropdetection circuit subsequently determines whether the output voltagedrops abnormally according to the decreasing speed of the outputvoltage, so as to subsequently determine whether or not the shortcircuit occurs.
 2. The power converter of claim 1, wherein the abnormalvoltage drop detection circuit includes: a voltage comparison circuitfor determining whether or not the short circuit occurs according to acomparison result between the output voltage and a reference voltage. 3.The power converter of claim 2, wherein the reference voltage isadjustable.
 4. The power converter of claim 3, wherein: when the powerconverter is coupled to the electronic device through the cable, thereference voltage is set to a relatively lower level; and when the powerconverter is not coupled to the electronic device through the cable, thereference voltage is set to a relatively higher level.
 5. The powerconverter of claim 1, wherein the power converter includes an isolatedtype AC-DC converter, and the isolated type AC-DC converter transmits afeedback signal related to the output voltage to the switch control unitvia a feedback circuit, wherein the temporary stop signal disables theswitch control unit by turning off the feedback circuit.
 6. The powerconverter of claim 1, wherein the timer circuit generates the temporarystop signal by one or a combination of two or more of the followingapproaches: generating the temporary stop signal STOP during orimmediately after a start-up operation; generating the temporary stopsignal STOP during or immediately after a power-on-reset operation;generating the temporary stop signal STOP periodically; or generatingthe temporary stop signal STOP irregularly.
 7. A short circuit detectionmethod of a power supply system, wherein the power supply systemincludes a power converter for converting an input voltage to an outputvoltage to be supplied to an electronic device through a cable; theshort circuit detection method of the power supply system comprising thesteps of: stopping converting the input voltage to the output voltagefor a disable time period in which a switch control unit of the powerconverter has been disabled; after the switch control unit has beendisabled, subsequently determining whether the output voltage dropsabnormally according to a decreasing speed of the output voltage, so asto subsequently determine whether or not a short circuit occurs.
 8. Theshort circuit detection method of the power supply system of claim 7,wherein the step of determining whether or not the short circuit occursaccording to the decreasing speed of the output voltage includes:comparing the output voltage with a reference voltage.
 9. The shortcircuit detection method of the power supply system of claim 8, whereinthe reference voltage is adjustable.
 10. The short circuit detectionmethod of the power supply system of claim 9, wherein: when the powerconverter is coupled to the electronic device through the cable, thereference voltage is set to a relatively lower level; and when the powerconverter is not coupled to the electronic device through the cable, thereference voltage is set to a relatively higher level.
 11. The shortcircuit detection method of the power supply system of claim 7, whereinthe power converter includes an isolated type AC-DC converter, and theisolated type AC-DC converter transmits a feedback signal related to theoutput voltage to a switch control unit via a feedback circuit, whereinthe step of stopping converting the input voltage to the output voltagefor a disable time period includes: disabling the switch control unit byturning off the feedback circuit.
 12. The short circuit detection methodof the power supply system of claim 7, wherein the step of stoppingconverting the input voltage to the output voltage for a disable timeperiod includes: starting the disable time period during or immediatelyafter a start-up operation; starting the disable time period during orimmediately after a power-on-reset operation; starting the disable timeperiod periodically; or starting the disable time period irregularly; ora combination of two or more of the above.